Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Low Pass RC filter

Status
Not open for further replies.

Scarr

Member
I want to stop any noise above 50Hz on a line, I have played with some caps and resistors and some online calculators but can't seem to get the values correct! The line is 12v DC can any suggest a RC pair that will work

Thanks

Steve
 
Last edited:
You can't stop noise but you can reduce it an arbitrary amount depending on the filter order. How much current must the filter carry?
 
Hi crutschow,

Enough to have a Arduino Due detect a low/high transition I would think a few mA would be fine

Thanks

Steve
 
Hi

A passive low pass RC filter should do something anyway. You have to see how high a value R can take in your application and not bother anything else. Once you determine that, you can add additional stages easily if needed by dividing that R up between the stages.

For example, if you determine that R=10 is the maximum value your application can take, then for one stage you use R=10 and some large capacitor like 100uf or even 1000uf. If that's not enough, to add another stage divide R by 2 which gives us 5 ohms for each stage, and keep the capacitor value the same (like 100uf to 1000uf or more). If that's not enough, then divide the original R by 3 and add anther stage. Since the original R was 10 ohms, the new R is 3.33 ohms and you use three stages. For four stages, R would be 10/4=2.5 ohms, and for five stages 10/5=2 ohms for each resistor.

Keeping the cap the same value for all the caps ensures you get more cut in the noise, and keeping the total series value of R the same as the original means you dont cut the DC value which the application needs to work properly.

Also, a series inductor can work wonders for this kind of thing. A small inductor in series with the cap makes a single stage cut much better. You do have to be more careful though because when the power turns off there is a chance that the inductor can develop a high voltage which could blow out various parts of the circuit. It depends on several factors how bad this can be.
 
A digital filter will work as long as there's no aliased noise (that above 1/2 the A/D sample frequency).

What is the frequency and amplitude of the noise?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top